1. Field of the Invention
The present invention relates to an optical recording medium such as an optical disk, and more specifically it relates to an optical recording medium with improved recording density, which is formed by the lamination of different recording layers in one and the same recording medium, and a recording/playback apparatus therefor.
2. Description of the Related Art
Research into external memory devices which have the high-speed access ability of a computer magnetic disks have and the large storage capacity of an optical disks have, is progressing at a rapid pace.
It is said to be certain that a next-generation disk apparatus, for reasons such as high-speed transfer rate, high-speed random access, usability of medium with mass-storage memory, and non-contact structure to provide long life, will be an optical disk apparatus. In the past, there have been various types of optical disks, such as magneto-optical disks and phase-change disks, all of these being based on a single recording and playback method, so that one piece of information is recorded at a given location on the disk.
In recent years, to improve the storage capacity of such media, there has been proposed the lamination of recording layers with different information recording/playback methods in one and the same disk, so that by picking up multiple channels of recording information on such recording layers, respectively, it is possible to record two or more pieces of information in the same location on the disk. For example, in Japanese Unexamined Patent Publication (KOKAI) No.63-257946, there is a proposal for one disk a surface of which is divided into at least two areas and an optical recorded layer and a magnetic recording layer are parallely formed in the respective area. In Japanese Unexamined Patent Publication (KOKAI) No. 2-91841, there is a proposal of a disk in which an optical phase-change pit-structure array on which ROM information is registered, is provided on a surface of the disk and an magneto-optical layer, which can store RAM information thereon, is formed on the optical phase-change pit structure array so that the optical phase-change pit structure array and the magneto-optical layer are integrally combined into one disk. Further, in Japanese Unexamined Patent Publication (KOKAI) No. 3-40247 is a proposal of an optical disk of on which a magneto-optical recording layer and Japanese Unexamined Patent Publication (KOKAI) No. 5-12751, is a proposal of a phase-change recording layer are also stacked.
While it is possible, in this manner, by laminating different recording layers, to increase the recording density, in a medium as shown in the Japanese Unexamined Patent Publication (KOKAI) No.63-257946, in which the above-noted optical recording layer and magnetic recording layer are formed on one surface of a disk in respectively separated areas, it is necessary to have separate heads for recording and for playback of information. This makes the optical recording/playback apparatus complex, and in the case of integrating an optical phase-change pit structure with an magneto-optical recording layer, as shown in the Japanese Unexamined Patent Publication (KOKAI) No. 2-91841, it is difficult to overwrite the optical phase-change pit structure.
With regard to this point, there is an advantage to the medium formed by laminating a magneto-optical recording layer and a phase-change recording layer to each other, in that a single optical head can be used for both recording and playback of information.
However, in a range of the Japanese Unexamined Patent Publication (KOKAI) No.3-40247 because the magneto-optical recording layer and the phase-change recording layer are formed in different grooves (tracking grooves) on the disk, respectively, it is not possible at a given location to record both information which should be registered onto each of the recording layers, this being disadvantageous in terms of increasing the storage capacity. In the Japanese Unexamined Patent Publication (KOKAI) No. 5-12751, there is no description of what type of structure the magneto-optical recording layer and the phase-change recording layer are laminated into, the disclosure instead concerning how information different from each other should be registered at the same place but in different recording layers from each other and how it should be playbacked, and not being sufficient to enable practice thereof.